Electron beam tube



Nov. 12, 1957 R. E. BYRAM ETAL 2,813,209

ELECTRON BEAM TUBE Filed Sept. 30, 1954 /i 1 If I L/ I /7 I"| I I I 1,.

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United States Patent Ofilice 2313209 Patented Nov. 12, 1957 ELECTRONBEAM TUBE Robert E. Byram and Arthur P. Sweet, Jr., Lancaster,

Pa., assignors to Radio Corporation of America, a corporation ofDelaware This invention relates to an electron beam tube and moreparticularly to an anode structure for an electron beam'tube having theanode thereof sealed to an end of the tube. The invention provides anelongated electron tube which has beam forming means at one end thereof.A tubular anode, having a target plate therein adapted to withstandheating to incandescence by bombardment of an electron beam, is sealedinto the tube envelope at the other end of the tube. The anode of theinvention provides sufficient thermal insulation between the targetplate and the anode-envelope seal to prevent excessive sealtemperatures. Such a tube is particularly adapted to be operated at arelatively high anode potential. The anode structure described isillustrated but not claimed in copending application Serial No. 456,215filed September 15, 1954, of R. D. Reichert and assigned to the sameassignee as the present invention.

In certain types of electron tubes, for example in high voltagerectifiers or shunt regulator triodes, it is advantageous to support theanode from the envelope at an end of the tube remote from the otherelectrodes for insulation purposes. It is also desirable to reduce thevoltage gradient at the more negative portions of the tube to reducecold emission problems. This reduction in voltage gradient can best beaccomplished by employing beam forming means to provide an electron beamdirected at the anode. When it is also necessary to dissipate arelatively large amount of energy at the anode, and the energy isconcentrated at a relatively small region in the anode, a problem ofheat dissipation arises. The

relatively high anode voltages also give rise to hard X-ray radiationwhich may constitute a health hazard.

One way of obtaining anode heat dissipation and of reducing relativelyhigh anode temperatures is by increasing the anode area. However, if theheating occurs at a relatively small area of the anode it is alsonecessary to increase the mass of the anode to conduct heat to thelarger radiating area. A relatively massive anode is objectionable inthe tube described as it puts a strain on the anode-envelope seal and onthe envelope of the tube. An anode capable of a relatively high thermaldissipation by the means of increased anode mass and area requiresrelatively heavy supports. The increased anode mass renders the sealvulnerable to cracking due to strains placed on it by the inertia of theanode during the normal handling of the tube.

Accordingly, it is an object of the invention to provide an improvedelectron beam tube having an anode with a portion thereof adapted to beoperated at a relatively high temperature.

It is another object of the invention to provide an electron beam tubehaving an improved anode which is sealed to the tube envelope at one endthereof and which is adapted to receive a relatively dense, highvelocity electron beam at a target plate therein without substantiallyheating the tube envelope at the sealed end.

It is a further object of the invention to provide an improved electronbeam tube adapted to be operated at relatively high anode voltageswithout producing hard X-ray radiation outside the tube.

The invention provides an improved electron tube having beam formingmeans at oneend of the tube and adjacent a base thereof. An anode issealed through the envelope at the other end. The beam forming means maycomprise a cathode and means for forming an electron lens to shape astream of electrons, accelerated from the cathode to the anode, into arelatively narrow beam. The anode, which is spaced along the path of theelectron beam from the beam forming means, has a tubular member aroundthe axis defined by the beam and a target plate within a portion ofthemember intermediate the ends thereof. Thus the target plate ispositioned in the path of the electron beam. The target plate interceptsthe electron beam so that the beam dissipates substantially all of itsenergy at that plate. The beam raises the plate, and the portions of themember adjacent to the plate, to incandescence. The tubular member hasabout two-thirds of its length disposed between the target plate and theend of the tube through which the anode is sealed. The portion of themember remote from the beam forming means provides a support of lowthermal conductivity such that the portion of the anode adjacent to theanode-envelope seal remains at a relatively low temperature. The portionof the member adjacent to the beam forming means acts as a shield toprevent the X-rays generated at the target plate from passing outsidethe tube.

While the invention is pointed out with particularity in the appendedclaims it may be best understood from the following detailed descriptionand drawing. The embodiment described is presented solely forillustrative purposes and not by way of limitation.

The drawing shows a side elevation partly in section of an electron beamtube embodying the invention.

The electron beam tube 1 includes an elongated, evacuated envelope 2.Prongs 3 extend from a base 4 at one end of the envelope. The tube maybe supported in a tube socket (not shown) by means of these prongs andsome of the internal tube elements may be electrically connected to thesocket by the prongs.

Beam forming means 5 are provided within the envelope 2 at the endthereof adjacent the base 4. The beam forming means may include athermionic cathode 6 and an apertured shield cup 7 which encloses thecathode. The shield cup is adapted to be biased at substantially thesame potential as the cathode so as to form an electron lens at theaperture 8 therein. A screen 9 may be stretched across the aperture 8 toform a grid across the electron lens for controlling the beam current.The electron lens thus focuses a stream of electrons from the cathodethrough the grid and in the form of a beam 10. The path of the beamextends into an anode 11 which is sealed to the end of the enveloperemote from the base.

The anode 11 includes a tubular member 12 around the path of the beam16. The tubular member is spaced along the beam path from the beamforming means 5 and is fixed to an anode lead cap 13 which extendsthrough an anode-envelope seal 34-. The anode lead cap may be providedwith a number of apertures 15 at a portion thereof within the envelopeand adjacent the seal. These apertures serve to reduce the conduction ofheat between material must be mechanically strong and have low vaporpressure at this temperature. Tantalum, which has a relatively low vaporpressure, has proven ideally suited for a target plate. Tantalum alsoexhibits gettering action at the aforementioned temperature so that thetarget plate itself getters gases released within the anode. The tubularanode member which supports the target plate is of a material, such asstainless steel, which exhibits a relatively high structural strengthand which has a relatively high thermal resistivity suflicient toprevent heat from the target plate from being immediately conducted tothe anode-envelope seal. During normal tube operation the portion of thetubular member adjacent the target plate is also heated to a relativelyhigh temperature. Consequently, it is also desirable to provide agettering action around the region of the outside of the member inregistry with the target plate. A band 17 of getter material such aszirconium is provided around the member for that purpose.

It will be apparent from the foregoing description that a novel electronbeam tube is provided which is particularly adapted to be used inrelatively high voltage applications. A tube using the improved anodestructure described is capable of relatively high heat dissipation witha relatively low anode mass.

What is claimed is:

1. An electron beam tube having an elongated envelope containing at oneend thereof beam forming means for producing a focused electron beamalong a beam axis, and sealed to the other end thereof an anode aroundsaid axis and spaced from said beam forming means, said anode includinga tubular member having an open end thereof facing said beam formingmeans and being of a material characterized by a relatively high thermalresistivity, and a target plate within and across a portion of saidmember intermediate the ends thereof and disposed closer to said openend than to the other end of said member so that substantially all ofthe energy of said beam is dissipated at said plate, said plate beingthermally insulated from said envelope to an extent sufficient toprevent overheating of said envelope and forming a shield for shieldingsaid envelope from hard X-ray radiation produced by the bombardment ofsaid plate by said beam.

2. An electron beam tube having an elongated envelope containing at oneend thereof a cathode and lens forming means adjacent said cathode forproviding an electron lens for producing a focused electron beam along abeam axis, an anode sealed to the other end of said envelope and havinga portion thereof around said axis and spaced from said electron lens,said anode including a tubular member having an open end thereofadjacent said electron lens and being of a material characterized by arelatively high thermal resistivity, and a substantially cup-shapedtarget within and across a portion of said member and spaced from eachof the ends of said memher a distance equal to at least about one-thirdof the distance represented by the length of said member, said cupshapedtarget having an open end thereof facing said electron lens wherebysubstantially all of the energy of said beam is dissipated within saidtarget without overheating said other end of said envelope.

3. An electron beam tube having an elongated envelope containing at oneend thereof beam forming means for producing an electron beam along abeam axis, an anode sealed to the other end of said envelope and havinga portion thereof around said axis and spaced from said beam formingmeans, said anode including a substantially tubular member having anopen end thereof adjacent said beam forming means and being of amaterial characterized by a relatively high thermal resistivity, and asubstantially cup-shaped target within and across a portion of saidmember and spaced along said member from said other end of saidenvelope, said cup-shaped target having the open end thereof facing saidbeam forming means whereby substantially all of the energy of said beamis dissipated at said target, the distance between the end of saidmember adjacent said beam forming means and said target being about halfthe distance between the end of said member remote from said beamforming means and said target whereby said target is thermally insulatedfrom said envelope to an extent sufficient to prevent overheating ofsaid envelope.

4. An electron beam tube having an elongated envelope containing at oneend thereof a cathode and lens forming means adjacent said cathode forproviding an electron lens for producing a focused electron beam along abeam axis, an anode sealed to the other end of said envelope and havinga tubular member around said axis and spaced along said axis from saidlens forming means, said tubular member having an open end thereofadjacent said electron lens and being of a material characterized by arelatively high thermal resistivity, and a substantially cup-shapedtarget within and across a portion of said member and spaced along saidmember from said other end of said envelope, said cup-shaped targethaving an open end thereof facing said electron lens wherebysubstantially all of the energy of said beam is dissipated within saidtarget without overheating said other end of said envelope and being ofa material including tantalum so that said target effects a getteringaction within said tube at portions thereof adapted to be heated to arelatively high temperature.

5. An electron beam tube having an elongated envelope containing at oneend thereof beam forming means for producing a focused electron beamalong a beam axis, an anode sealed to the other end of said envelope andhaving a portion thereof around said axis and spaced from said beamforming means, said anode including a tubular member having an open endthereof adjacent said beam forming means and being of a materialcharacterized by a relatively high thermal resistivity, and a targetplate within and across a portion of said member so that substantiallyall of the energy of said beam is dissipated at said plate, said platebeing spaced along said member from said other end of said envelopewhereby said plate is thermally insulated from said envelope to anextent sufficient to prevent overheating of said other end of saidenvelope and being of a material characterized by a relatively low vaporpressure and relatively good gettering properties at the temperatureattained by said plate during normal tube operation whereby gasesreleased within said envelope are absorbed by said plate.

6. An electron beam tube having an elongated envelope containing at oneend thereof beam forming means for producing a focused electron beamalong a beam axis, an anode sealed to the other end of said envelope andhaving a portion thereof around said axis and spaced from said beamforming means, said anode including a tubular member having an open endthereof adjacent said beam forming means and being of a materialcharacterized by a relatively high thermal resistivity, a target platewithin and across a portion of said member so that substantially all ofthe energy of said beam is dissipated at said plate, said plate beingspaced along said member from said other end of said said envelopewhereby said plate is thermally insulated from said envelope to anextent sufficient to prevent overheating of said other end of saidenvelope and being of a material characterized by relatively goodgettering properties at the temperature attained by said plate duringnormal tube operation, and a getter band around said tubular member at aportion thereof in'reg-.

istry with said plate within said member, whereby gettering action isprovided at the portions of the tube adapted to be heated to arelatively high temperature by the dissipation of the beam energy atsaid plate.

7. An electron beam tube including an envelope having beam forming meansat one end thereof for producing a focused electron beam, asubstantially tubular anode characterized by a relatively high thermalresistivity and sealed at one end thereof to the other end of saidenvelope, and a substantially cup-shaped target within and across aportion of said anode intermediate the ends thereof and in a position toreceive said beam and disposed closer to the end of said anode adjacentto said beam forming means than to said one end of said anode, wherebysubstantially all of the energy of said beam is dissipated at saidtarget without overheating said envelope.

References Cited in the file of this patent UNITED STATES PATENTS2,223,908 Bull Dec. 3, 1940 2,269,845 Dailey Jan. 13, 1942 10 2,269,852Hummel Jan. 13, 1942 2,412,998 Litton Dec. 24, 1946 2,558,357 Grimm June26, 1951

